Over the course of a number of years, I gathered a great deal of information about the internals of the HP-48 calculator. The result of this research led to the creation of this guide. It also includes some ASCII schematics of the HP-48 internals (down to the pin level), collected by Philippe Teuwen.

Abstract

The purpose of this guide is to be the most comprehensive and detailed guide to the operation of the Saturn processor, useful for anyone trying to write and optimize ML code, use some of the chip tricks or just to gain an understanding of how the chip works.

Download: saturn.txt